The main aim of this research project is to further the understanding of the genetics of antigenic differences detected primarily on human white cells, but also on the other human tissues. Most of the antigens so far described belong to one major histocompatibility system called HL-A. Many specificities within this system, however, remain to be clearly identified and we shall continue our search for new antigens. At the same time we shall extend our population studies of the HL-A antigens. These are directed at establishing the generality of the patterns of association found in Caucasian populations, finding new specificities unique to given populations and making use of the HL-A polymorphism for population genetic and anthropological studies. Studies on the use of animal sera, in particular from cattle, for the detection of human iso-antigens belonging to HL-A and other systems will be continued and extended. The use of human-mouse hybrid cell lines to immunize appropriate mouse strains will also be explored as a potential way of making interesting new sera. Projected technical developments include attempts to remove anti-complementary activity by column fractionation, improvement of short term cell storage procedures, comparisons between mixed agglutination, complement fixation and cytotoxicity assays and further development and refinement of our computer programs for the analysis of white cell antigen data.